Editing Java virtual machine (section)

===Class loader===
{{Main|Java class file}}
One of the organizational units of JVM byte code is a [[Class (computer programming)|class]]. A class loader implementation must be able to recognize and load anything that conforms to the Java class [[file format]]. Any implementation is free to recognize other binary forms besides ''class'' files, but it must recognize ''class'' files.

The class loader performs three basic activities in this strict order:

#Loading: finds and imports the binary data for a type
#Linking: performs verification, preparation, and (optionally) resolution
#*Verification: ensures the correctness of the imported type
#*Preparation: allocates memory for class variables and initializing the memory to default values
#*Resolution: transforms symbolic references from the type into direct references. 
#Initialization: invokes Java code that initializes class variables to their proper starting values.

In general, there are three types of class loader: bootstrap class loader, extension class loader and System / Application class loader.

Every Java virtual machine implementation must have a bootstrap class loader that is capable of loading trusted classes, as well as an extension class loader or application class loader. The Java virtual machine specification does not specify how a class loader should locate classes.